I'm new to Virgo and OSGi. I have an existing Servlet application that runs on Tomcat. I want to move this application to VTS and let it have access to OSGi based services that I've created.

What is the recommended approach for a Web app to gain references to services? I have little to no experience with Spring, and we are looking to stay as close to OSGi standards as possible to allow us to run in different servers.

You could implement a BundleActivator to get access to a bundle context and get a reference to an OSGi service with it (or better use a ServiceTracker. Don't forget to declare the activator in the manifest file.